The major emphasis of this laboratory continues to be twofold: On the mechanisms of the immunologic release of the chemical mediators of immediate type hypersensitivity including histamine, slow reacting substance of anaphylaxis (SRS-A), and the eosinophil leukocyte chemotactic factor of anaphylaxis (ECF-A) from tissues or cells; and on the formation and characterization of humoral systems involved in the inflammatory response, such as complement and the bradykinin-forming sequence. The progress in each of these areas has been great and includes: the recognition of adrenergic and cholinergic controls of the antigen-induced release of chemical mediators from human respiratory tissues; the appreciation of an additional mediator of immediate type hypersensitivity, ECF-A, and the purification of SRS-A to a point permitting pathophysiologic studies; the demonstration that two immunochemically distinct rat immunoglobulins can mediate immediate type hypersensitivity reactions in vivo and in vitro; the observation that active Hageman factor and its fragments act on three distinct proenzyme substrates to elicit bradykinin-generation, fibrinolysis, and coagulation; a further analysis of the mechanisms of interaction, nature, and controls of the classical and alternate complement sequences; and the recognition and assessment of new factors which modulate polymorphonuclear leukocyte directed and random mobility, such as kallikrein, plasminogen activator, and the neutrophil immobilizing factor.